Methods and apparatus for coupling an earth terminal to a satellite

ABSTRACT

Methods and apparatus are provided for coupling an earth terminal to a satellite The apparatus comprises multiple inputs of the earth terminal configured to receive multiple digital communication signals, a autoscaling digital multiplexer of the earth terminal configured to digitally multiplex the multiple digital communication signals to produce a digital composite signal, and a digital modulator of the earth terminal configured to digitally modulate the digital composite signal to produce a digitally modulated composite signal. In addition, the apparatus comprises an input of the satellite configured to receive the digitally modulated composite signal, and a digital demodulator of the satellite configured to digitally demodulate the digitally modulated composite signal received by the input of the satellite to produce a second digital composite signal. Furthermore, the apparatus comprises a autoscaling digital demultiplexer of the satellite configured to digitally separate the second digital composite signal into a second plurality of digital communication signals, and a modulator of the satellite configured to modulate the second plurality of digital communications signal to produce multiple modulated analog signals.

BACKGROUND OF THE INVENTION

The present invention generally relates to satellite communicationsystems, and more particularly to apparatus and methods for coupling anearth terminal to a satellite.

Satellite-based communication systems have continued to evolve and havebecome an important component of modern society. Numerous applicationsare supported by satellite-based communication systems that provide widearea coverage, such as worldwide television, communications to remoteareas, wide area data networks, global personal communications tohand-held portable telephones, broadband voice, video, and/or data. Asthe number of applications supported by satellite-based communicationsystems has increased and the number of users using the applications hasincreased, processes have been developed to accommodate the increasednumber of applications and users.

One process that has been developed to accommodate the increased numberof applications and users is multiplexing. The process of multiplexingallows multiple signals to be sent on a single channel, and many formsof multiplexing have been developed to generate a multiplexedcommunication signal, including, but not limited to time multiplexing,frequency multiplexing, space multiplexing (e.g., Frequency-DivisionMultiplexing (FDM), Time-Division Multiplexing (TDM), Space-DivisionMultiplexing (SDM), Orthogonal Frequency Multiplexing (OFM),Code-Division Multiple Access (CDMA) multiplexing, Wideband CDMA (WCDMA)multiplexing, Time-Division Multiple Access multiplexing, OrthogonalFrequency Multiple Access (OFMA) multiplexing, and Frequency DivisionMultiple Access multiplexing (FDMA)). While multiplexing has increasedthe number of signals that can be sent on a single channel toaccommodate numerous applications and users, additional complicationsare introduced when multiplexing is utilized in satellite-basedcommunication systems.

For example, existing and proposed satellite-based communication systems(e.g., wideband CDMA Mobile Satellite Systems (MSS)) use an analog,frequency division multiplexed (FDM) channelized approach that maps eachdownlink beam and carrier, which is typically an L or S band carrier, toa specific gateway uplink frequency, which is typically a C, X or Kaband carrier. This analog FDM channelized approach directly couples theearth terminal uplink to the user downlink, so that fading or otherpower variation in the earth terminal uplink results in uncontrolledpower variations in the user downlink, thereby degrading the ability toaccurately set the user downlink power level. In addition, the use ofthe analog FDM channelized approach introduces nonlinearities, whichgenerally results in an increase in the noise floor due tointermodulation distortion, such that the presence of a few highcapacity, and hence high power beams, will undesirably increase thepower of other beams and channels. Furthermore, the introduction ofnonlinearities will also generally degrade power control as largecarrier codes will be affected to a greater extent than small carriercodes due to a tendency for the large carrier codes to become compressedprior to the small carrier codes. As can be appreciated by those ofordinary skill in the art, the foregoing effects reduce the likelihoodof implementing numerous tasks, such as digital beam forming, on thesatellite as the relative amplitude and phase characteristics betweenchannels, corresponding to different feed elements, are altered in aunpredictable manner.

To overcome issues such as power control and linearity, processingon-board the satellite has been proposed to generate the multiplexingsignal (e.g., CDMA signal). However, increasing the processing on-boardthe satellite typically increases the cost of the satellite.Furthermore, the initial configuration of the satellite to support aparticular multiplexing waveform (e.g., CDMA signal) is generallyunalterable during the lifetime of the satellite.

In view of the foregoing, it should be appreciated that it would bedesirable to provide apparatus and methods for coupling an earthterminal to a satellite that addresses the foregoing and otherdeficiencies of satellite-based communication systems that are notspecifically or inferentially addressed in this background of theinvention. Furthermore, additional desirable features provided by theinvention will become apparent to one skilled in the art from thedrawings, foregoing background of the invention, following detaileddescription of the drawings and appended claims.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, an apparatus is provided forcoupling an earth terminal to a satellite The apparatus comprisesmultiple inputs of the earth terminal configured to receive multipledigital communication signals, an autoscaling digital multiplexer of theearth terminal configured to digitally multiplex the multiple digitalcommunication signals to produce a digital composite signal, and adigital modulator of the earth terminal configured to digitally modulatethe digital composite signal to produce a digitally modulated compositesignal. In addition, the apparatus comprises an input of the satelliteconfigured to receive the digitally modulated composite signal, and adigital demodulator of the satellite configured to digitally demodulatethe digitally modulated composite signal received by the input of thesatellite to produce a second digital composite signal. Furthermore, theapparatus comprises a autoscaling digital demultiplexer of the satelliteconfigured to digitally separate the second digital composite signalinto a second plurality of digital communication signals, and amodulator of the satellite configured to modulate the second pluralityof digital communications signal to produce multiple modulated analogsignals.

In accordance with the present invention, a method is also provided forcoupling an earth terminal and a satellite. The method comprisesreceiving multiple digital communication signals with multiple inputs ofthe earth terminal, digitally multiplexing the multiple transformeddigital communication signals with an autoscaling digital multiplexer ofthe earth terminal to produce a digital composite signal, and digitallymodulating said digital composite signal with a digital modulator of theearth terminal to produce a digitally modulated composite signal. Inaddition, the method comprises receiving the digitally modulatedcomposite signal with an input of the satellite, digitally demodulatingthe digitally modulated composite signal with a digital demodulator ofthe satellite to produce a second digital composite signal, anddigitally separating the second digital composite signal multipledigital communications signals. Furthermore, the method comprisesmodulating the multiple digital communication signals with a modulatorof the satellite to produce multiple modulated analog signals.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe appended drawing figures, wherein like numerals denote likeelements, and:

FIG. 1 is a simplified illustration of a communication system accordingto a preferred exemplary embodiment of the present invention;

FIG. 2 is a simplified illustration the earth terminal of FIG. 1 havingan apparatus for coupling the earth terminal to a satellite according toa preferred exemplary embodiment of the present invention;

FIG. 3 is the autoscaling digital multiplexer of FIG. 2 according to apreferred exemplary embodiment of the present invention;

FIG. 4 is a method for encoding the scaling vector according to apreferred exemplary embodiment of the present invention;

FIG. 5 is another method for encoding the scaling vector according to apreferred exemplary embodiment of the present invention;

FIG. 6 is a simplified illustration the satellite of FIG. 1 having anapparatus for coupling the earth terminal to the satellite according toa preferred exemplary embodiment of the present invention; and

FIG. 7 is the autoscaling digital demultiplexer of FIG. 6 according to apreferred exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The following detailed description of a preferred embodiment is merelyexemplary in nature and is not intended to limit the invention or theapplication and uses of the invention. Furthermore, there is nointention to be bound by any theory presented in the precedingbackground of the invention or the following detailed description of thedrawings.

Referring to FIG. 1, a simplified illustration of a communication system100 is presented according to a preferred exemplary embodiment of thepresent invention. The subsequently described apparatus andcorresponding methods of the present invention are preferably utilizedin a satellite-based communication system. As can be appreciated by oneof ordinary skill in the art, the principles discussed herein can bereadily applied to numerous satellite-based, radio, cable television(CATV), telephony as well as other data, voice video or a combinationdata, video and/or voice communications systems. Furthermore, as can beappreciated by one of ordinary skill in the art, the principlesdiscussed herein can also be readily applied to other satellite-basedsystems such as RF monitoring and surveillance, direct finding, RADAR,and sonar.

The communication system 100 comprises at least one satellite 102, andpreferably comprises multiple satellites 102 forming a satelliteconstellation. The satellites 102 are preferably located ingeosynchronous orbits relative to a celestial body, such as the earth.However, the satellites 102 can be located in any number of orbitsrelative to a celestial body according to the present invention. Forexample, the satellites 102 can be located in a low earth orbit, mediumorbit, and/or a polar orbit as known to those of ordinary skill in theart.

The satellite 102 or satellites 102 of the communication system 100 areconfigured to couple an earth terminal 104 of the communication system100 to user equipment 106, other earth terminals (not shown), and/orother communication systems. The satellite 102 is preferably coupled tothe user equipment 106 with multiple beams and communication links inorder improve the link margin that is available with a single beam. Theearth terminal 104 is preferably configured to connect one or moreelements of the communication system 100 to other communication systems(not shown) or a network 108 or networks, such as public networks,cellular networks, and/or private networks (e.g., Public SwitchedTelephone Network (PSTN) and the Public Land Mobile Network (PLMN)). Inaddition, the earth terminal 104 is preferably coupled to the satellite102 with a digitally modulated composite signal 110.

Referring to FIG. 2, a simplified illustration is presented of an earthterminal 104 having an apparatus 200 for coupling the earth terminal 104to the satellite 102 as shown in FIG. 1 with a digitally modulatedcomposite signal 110 (i.e., providing an uplink from the earth terminal104 to the satellite according to a preferred exemplary embodiment ofthe present invention. Generally, the apparatus 200 comprises multipleinputs 202 of the earth terminal 104 that are configured to receivedigital communication signals and an autoscaling digital multiplexer 300that is configured to receive the digital communication signals receivedat the multiple inputs 202. The autoscaling digital multiplexer 300 isconfigured to digitally multiplex the digital communication signals andproduce a digital composite signal 206. A digital modulator 208 of theearth terminal 104 is configured to digitally modulate the digitalcomposite signal 206 to produce the digitally modulated composite signal110.

The digital communication signals received at the multiple inputs 202are preferably binary encoded analog waveforms that can be generatedusing digital signal processing techniques known to those of ordinaryskill in the art. The digital communication signals preferably representreceived analog signals that are digitally encoded, modulated, spread,and/or multiplexed information streams. According to a preferredembodiment of the present invention, the digital communication signalsare Third Generation Partnership Project (3GPP) Wideband Code DivisionMultiple Access (WCDMA) Direct Sequence Spread Spectrum (DSSS) signalscontaining multiple data and/or voice users using different spreadingcodes. However, the present invention is applicable to digitalcommunication signals in other modulation and multiple access schemesbased upon spread-spectrum communication, such as Code Division MultipleAccess (CDMA), Frequency Division Multiple Access (FDMA), Time DivisionMultiple Access (TDMA), or the like.

In accordance with a preferred embodiment of the present invention, thedigital communication signals received at the multiple inputs 202 areprovided to a digital transform matrix 210 prior to the digitalmultiplexing by the autoscaling digital multiplexer 300. The digitalcommunication signals received at the multiple inputs 202 are preferablyprovided to the digital transform matrix 210 for signal powerdistribution from one input to multiple outputs in a predetermined phaserelationship. The digital transform matrix 210 can be implemented withany number of matrices that distribute the signal power of the digitalcommunication signals from one input to multiple outputs. For example,the digital transform matrix 210 can be a Fourier transform matrix or aButler transform matrix. In addition, the digital transform matrix 210can have any number of dimensions, and preferably dimensions of N-by-M(N×M), where N and M are the number of inputs and outputs, respectively,and N and/or M is greater than or equal to two (2). Furthermore, thefunction provided by the digital transform matrix 210 is preferablyperformed at base band frequencies of the digital communication signalsusing combinatorial logic rather than performed on analog signals atRadio Frequencies (RF) using electromagnetic techniques provided bystrip line couplers.

As the digital transform matrix 210 is digitally implemented in thepreferred embodiment, it can be programmed for multiple configurationscorresponding to various digital transmitter and multiple-beam antennaconfigurations. An example of a digital transform matrix is described inU.S. Pat. No. 5,834,972, titled “METHOD AND SYSTEM IN A HYBRID MATRIXAMPLIFIER FOR CONFIGURING A DIGITIAL TRANSFORMER,” issued on Nov. 10,1998 to Schiemenz, Jr. et al, which is hereby incorporated by reference(hereinafter referred to as the “Schiemenz Reference”). The digitaltransform matrix 210 mathematically multiplies, multiplexes, andcombines the digital communication signals. As a result, while each ofthe digital communication signals may originally have significantvariations in peak magnitudes, the transformed digital communicationsignals 212 produced by the digital transform matrix 210 will preferablyhave reduced variations in the peak magnitudes as compared to thedigital communication signals originally provided to the digitaltransform matrix 210.

The transformed digital communication signals 212 generated by thedigital transform matrix 210 or the digital communication signalsreceived at the multiple inputs 202 are provided to the autoscalingdigital multiplexer 300 for multiplexing (i.e., sending the multipletransformed digital communication signals on the same channel). Theautoscaling digital multiplexer 300 can be implemented with any numberof multiplexing schemes in accordance with the present invention. FIG. 3illustrates a simplified illustration of the autoscaling digitalmultiplexer 300 according to a preferred exemplary embodiment of thepresent invention.

Referring to FIG. 3, the transformed digital communication signalsgenerated by the digital transform matrix 210 are provided to theprocessor 302 at processor inputs 304, which are coupled to the digitaltransform matrix outputs 303. The processor 302, which can beimplemented with software, hardware, or a combination of hardware andsoftware, receives the transformed digital communication signalspresented at the processor inputs 304 and determines the scaling vectorhaving an element (e.g., exponent) for each of the transformed digitalcommunication signals, which can be utilized to reduce the resolutionfor representing the transformed signal while providing a suitablefidelity. The processor 302 can determine each element of the scalingvector for each of the binary strings corresponding to the transformeddigital communication signals using any number of techniques known tothose of ordinary skill in the art, which convert each of the binarystrings to a digital floating point representation (i.e., sign bit,exponent, mantissa) For example, a sixteen (16) bit binary string can berepresented with an eight (8) bit instantaneous fidelity with an eight(8) bit mantissa and a three (3) bit exponent. In addition, theprocessor 302 preferably evaluates the transformed digital communicationsignals for saturation conditions and corrects such saturation if such acondition exists as discussed in the Schiemenz Reference.

Once the scaling vector is determined by the processor 302, each of theelements of the scaling vector is provided by the processor 302 atprocessor outputs 306 for generation of a mantissa for each of thetransformed digital communication signals. The processor outputs 306 arecoupled to an operator 308, which preferably comprises one or moremultipliers in accordance with the present invention. However, one ofordinary skill in the art will recognize that if the exponents arelimited to powers-of-two, the operator 308 can be implemented in othermanners, such as a selector that selects the mantissa from a subset ofthe binary string, or with a shifter that conducts a shifting operationbased upon the exponent.

The operator 308 is also coupled to the digital transform matrix outputs303 such that the operator 308 receives the transformed digitalcommunication signals in addition to the scaling vector (i.e., elementsof the scaling vector) from the processor 302. Preferably, the digitaltransformed matrix outputs 303 are coupled to the operator 308 withdelays 310 to synchronize the transformed digital communication signalswith the scaling vector generated by the processor 302. The operationperformed by the operator 308 with the transformed digital communicationsignals and the scaling vector produces a mantissa for each of thetransformed digital communication signals at the operator outputs 312,which are coupled to multiplexer inputs 314 of a multiplexer 316. As canbe appreciated by one of ordinary skill in the art, the operator 308 canbe incorporated into the functions provided by the processor 308, andthe mantissa for each of the transformed digital communication signalscan be provided by the processor 302 to the multiplexer 316.

In addition to the mantissa for each of the transformed digitalcommunication signals, the multiplexer 316 is also configured to receivethe scaling vector from the processor 302. The scaling vector can beprovided to the multiplexer 316 in the form as presented to the operator308 or preferably encoded before it is provided to the multiplexer 316.More specifically, the processor 308 preferably encodes the scalingvector and produces an encoded scaling vector, which is provided at anencoded output 318 that is coupled to the multiplexer 316, andpreferably coupled to the multiplexer 316 with a delay 320 tosynchronize the encoded scaling vector and the corresponding mantissasproduced by the operator 308.

Referring to FIG. 4, a method 400 for encoding the scaling vector isillustrated according to a preferred embodiment of the presentinvention. The method 400 comprises determining the minimum exponent(E_(min)) of the scaling vector 402 and calculating the differencebetween each of the elements (e.g., exponents) of the scaling vector andthe minimum exponent 404 (i.e., E_(diff)=E−E_(min)). The method 400further comprises forming the encoded scaling vector from the minimumexponent and the differences between the exponents and the minimumexponent 406 (e.g., encoded scaling vector=[E_(min), E_(diff(1)),E_(diff(2)), . . . , E_(diff(N))], where N is the number of exponentscontained in the original scaling vector, which also corresponds to thenumber of transformed digital communication signals.)

Referring to FIG. 5, a second method 500 for encoding the scaling vectoris illustrated according to a preferred exemplary embodiment of thepresent invention. The method 500 comprises determining the maximumexponent (E_(max)) of the scaling vector 502 and calculating thedifference between the maximum exponent and each of elements (e.g.,exponents) of the scaling vector 504 (i.e., E_(diff)=E_(max)−E). Themethod further comprises forming the encoded scaling vector from themaximum exponent and the differences between the maximum exponents andeach of the exponents of the scaling vector 506 (e.g., encoded scalingvector=[E_(min), E_(diff(1)), E_(diff(1)), E_(diff(2)), . . . ,E_(diff(N))], where N is the number exponents contained in the originalscaling vector, which also corresponds to the number of transformeddigital communication signals.)

As can be appreciated by one of ordinary skill in the art, the peakamplitude of each of the transformed digital signals are substantiallysimilar and the bandwidth preferably provided to transmit the scalingvector will be less than or equal to the product of the bitsrepresenting the scaling vector and the number of inputs to theautoscaling digital multiplexer 300. For example, four (4) bits ofdynamic range may be desirable, but each of the inputs to theautoscaling digital multiplexer can be scaled with the selection of asingle four (4) bit scaling element and selection of a one (1) bitscaling element for each of the inputs to identify if the exponent ofeach of the inputs is greater than the single four (4) bit scalingelement. Therefore, the scaling vector is provided with the number ofbits of dynamic range (D) plus the number of input (N) (i.e., D+N).

In accordance with another embodiment of the present invention, methodsand apparatus that are well known to those of ordinary sill in the artcan be utilized for encoding the scaling vector. For example, Huffman,Elias, Lempel-Ziv (e.g., LZW and LZ77) methods can be utilized inaccordance with the present invention as well as adaptive methodsimplemented by Lynch-Davisson codes or Rissanen MDL. Furthermore,predictive encoding methods can be utilized in accordance with thepresent invention to select the encoding method and method parametersbased upon present and past signal statistics and other constraints suchas processing limitations, signal quality, and/or update latency, or thelike, to produce the encoded scaling vector. (See U.S. Pat. No.4,558,302, titled “HIGH SPEED DATA COMPRESSION AND DECOMPRESSIONAPPARATUS AND METHOD,” issued on Dec. 10, 1985 to Welch, which is herebyincorporated by reference; U.S. Pat. No. 4,701,745, titled “DATACOMPRESSION SYSTEM,” issued on Jan. 20, 1987 to Waterworth, which ishereby incorporated by reference; L. D. Davisson, UNIVERSAL NOISELESSCODING, IEEE Transactions on Information Theory, Vol. 19, No. 6, pp.783-795, 1973, which is hereby incorporated by reference; T. J. Lynch,SEQUENCE TIME CODING FOR DATA COMPRESSION, Proc. IEEE, Vol. 54, pp.1490-1491, October 1966, which is hereby incorporated by reference;Peter Elias, UNIVERSAL CODEWORD SETS AND REPRESENTATIONS OF THEINTEGERS, IEEE Transactions on Information Theory, Vol. 21, No. 2, pp.194-203, March 1975, which is hereby incorporated by reference; David A.Huffman, A METHOD FOR CONSTRUCTION OF MINIMUM REDUNDANCY CODES, InProceedings of the Institute of Radio Engineers, Vol. 40, pp. 1098-1101.Institute of Radio Engineers, September 1952, which is herebyincorporated by reference; Jorma Rissanen, UNIVERSAL CODING,INFORMATION, PREDICTION, AND ESTIMATION, IEEE Transactions onInformation Theory, Vol. 30, No. 4, pp. 629-636, July 1984, which ishereby incorporated by reference; Jorma Rissanen and Jr. Glen G.Langdon, UNIVERSAL MODELING AND CODING, IEEE Transactions on InformationTheory, Vol. 27, No. 1, pp. 12-23, January 1981, which is herebyincorporated by reference; Jacob Ziv and Abraham Lempel, A UNIVERSALALGORITHM FOR SEQUENTIAL DATA COMPRESSION, IEEE Transactions onInformation Theory, Vol. 23, No. 3, pp. 337-343, May 1977, which ishereby incorporated by reference; Jacob Ziv and Abraham Lempel,COMPRESSION OF INDIVIDUAL SEQUENCES VIA VARIABLE-RATE CODING, IEEETransactions on Information Theory, Vol. 24, No. 5, pp. 530-536,September 1978, which is hereby incorporated by reference.)

Referring to FIG. 3, and as previously described in this detaileddescription of the drawings, the encoded scaling vector or the scalingvector and the mantissa for each of the transformed digitalcommunication signals are provided to the multiplexer 316 formultiplexing (i.e., sending the multiple transformed digitalcommunication signals on the same channel). The multiplexer 316 canimplement any number of multiplexing schemes in accordance with thepresent invention. For example, and according to a preferred embodimentof the present invention, a TDM scheme is used to interleave the bits orgroups of bits. However, the present invention is applicable to othermultiplexing schemes such as TDMA, FDMA, FDM, OFDM, OFDMA, CDMA andwavelength multiplexing as well as using packet labeling schemes thatuse different addresses to identify the different multiplexed signalssuch as Multiprotocol Label Switching (MPLS) or Asynchronous TransferMode (ATM). The digital composite signal 206 generated by themultiplexer 316 is provided at the autoscaling digital multiplexeroutput 322. The digital composite signal 206 provided at the autoscalingdigital multiplexer output 322 is preferably encrypted according to thepresent invention.

Referring to FIG. 2, the digital composite signal 206 generated by theautoscaling digital multiplexer 300 is preferably encrypted by anencryptor 214. The encryptor 214 generally provides increased securityfor the digitally modulated composite signal 110 with a randomscrambling of the binary data stream. Any number of encryptiontechniques known to those of ordinary skill in the art can be used,include DES, triple DES, AES, Kusami, linear recursive shift sequences,and non-linear recursive shift sequences.

The encrypted digital composite signal 216 generated by the encryptor214 or the digital composite signal 206 produced by the autoscalingdigital multiplexer 204 is provided to the digital modulator 208, whichis configured to digitally modulate the encrypted digital compositesignal 216 or the digital composite signal 206 to produce the digitallymodulated composite signal 110. More specifically, the digital modulator208 digitally modulates the encrypted digital composite signal 216 orthe digital composite signal 206 onto one or more carries andpolarizations to produce the digitally modulated composite signal 110.The digital modulator 208 is preferably selected to provide a desiredbandwidth efficiency and hence capacity, with a pre-selected linkavailability. For example, according to a preferred embodiment of thepresent invention, one or more carriers with two polarizations, eachcontaining an 8PSK waveform and a block code, is used at a Ka band.However, any number of modulation schemes can be used according to thepresent invention, such as trellis encoded 8PSK; 16QAM or higher levelsof QAM using convolution, block, or block product codes suitable forturbo decoding. Once the digitally modulated composite signal isproduced by the digital modulator 208, it is preferably post-processedand preferably transmitted with a single or multiple antennaconfigurations (not shown).

Referring to FIG. 6, a simplified illustration of a satellite 102 havingan apparatus 200 for coupling the earth terminal 104 as shown in FIG. 2to the satellite 102 with the digitally modulated composite signal 110(i.e., providing an uplink from the earth terminal to the satellite) isillustrated according to a preferred exemplary embodiment of the presentinvention. Generally, the apparatus 200 comprises an input 602 of thesatellite 102 that is configured to receive the digitally modulatedcomposite signal 110 and a digital demodulator 604 of the satellite 102that is configured to digitally demodulate the digitally modulatedcomposite signal to produce a second digital composite signal 606generally corresponding to the digital composite signal 206 of FIG. 2.In addition, the apparatus 200 also comprises a autoscaling digitaldemultiplexer 700 of the satellite 102 that is configured to digitallyseparate the second digital composite signal 606 to produce a secondplurality of digital communication signals 610 generally correspondingto the plurality of digital communication signals received by the inputsof the earth terminal 104 as described with reference to FIG. 2.Furthermore, the apparatus 200 comprises a modulator 612 of thesatellite 102 that is configured to modulate the second plurality ofdigital communication signals 610 to produce a plurality of modulatedanalog signals 614. Lastly, the apparatus 200 preferably comprises adecryptor 616 that decrypts the encrypted encrypted digital compositesignal 216 generated by the encryptor 214 of FIG. 2, if such anencryptor 214 is utilized by the earth terminal 104.

As previously described in this detailed description of the drawings,the digitally modulated composite signal 110 received at the input 602of the satellite 102 is provided to the digital demodulator 604, andprovided to the digital demodulator 604 after decryption if thedigitally modulated composite signal 110 was originally encrypted at theearth terminal. More specifically, the digital demodulator 604 digitallydemodulates the digitally modulated composite signal 110 from the one ormore carriers and polarizations, as originally modulated by the digitalmodulator 208 of the earth terminal as described with reference to FIG.2, to produce the second digital composite signal 606 generallycorresponding to the digital composite signal 206 of FIG. 2.

Once the second digital composite signal 606 is produced by the digitaldemodulator 604, the second digital composite signal 606 is provided tothe autoscaling digital demultiplexer 608 for demultiplexing (i.e.,separating the second digital composite signal transmitted on the samechannel into the multiple digital communication signals) The autoscalingdigital demultiplexer 700 can be implemented with any number ofdemultiplexing schemes corresponding to the multiplexing schemeimplemented by the autoscaling digital multiplexer 300 of FIG. 2 inaccordance with the present invention. FIG. 7 illustrates a simplifiedillustration of the autoscaling digital demultiplexer 700 according to apreferred exemplary embodiment of the present invention.

Referring to FIG. 7, the second digital composite signal received at themultiplexed input 702 is provided to a demultiplexer 704 to separate(i.e., demultiplex) the mantissas and the encoded scaling vector.Preferably, the demultiplexer 704 separates the mantissas and theencoded scaling vector, which is provided to a processor 712 at aprocessor input 714 that is coupled to a demultiplexer output 716. Theprocessor 712, which can be implemented with software, hardware, or acombination of hardware and software, receives the encoded scalingvector and decodes the encoded scaling vector to produce the scalingvector for each of the mantissas (i.e., produces the exponent for eachof the mantissas. The decoding operation performed by the processor 712corresponds to encoding scheme used by the processor 302 described withreference to FIG. 3. For example, the decoding operation for theencoding method describe with reference to FIG. 5 would comprise addingthe difference for each element to the minimum exponent and the decodingoperation for encoding method described with reference to FIG. 6 wouldcomprise subtracting the difference for each element from the maximumexponent. However, these examples are not intended to limit theinvention as other decoding operations are within the scope of thepresent invention.

Once the scaling vector is decoded by the processor 712 or the scalingvector that was not originally encoded is produced by the demultiplexer,the scaling vector and the mantissa are provided to an operator 706,which in a preferred embodiment comprises one or more multipliers. Theoperator 706 is coupled to processor outputs 718 and/or thedemultiplexer outputs 720 to receive the scaling vector and themantissas, and the operator 706 produces the digital communicationsignals for each of the mantissas and the corresponding scaling vectorsat operator outputs 722. Preferably, the operator 706 is coupled to thedemultiplexer outputs 720 with delays 721 to synchronize the digitalmantissas produced by the demultiplexer 704 with the decoded scalingvector produced by the processor 712 if such decoding is performed bythe processor 712.

Referring to FIG. 6, the outputs of the autoscaling digitaldemultiplexer 700 are coupled to the inputs of the modulator 612 that isconfigured to modulate the second plurality of digital communicationsignals 610 to produce a plurality of modulated analog signals 614. Themodulator 612 converts the digital baseband representation to themodulated signal for transmission over communications link 114 as shownin FIG. 1. For example, digital communications signal at the multipleinputs 202 are preferably binary encoded baseband representation ofWCDMA signals, and modulator 612 preferably converts digitalcommunication signals 610 to the analog representation of the WCDMAsignal that is modulated onto a MSS L-band carrier frequency, which haveminimal distortion from the signal present at the multiple inputs 202.The modulator 612 can be realized using one of several techniques knownto those of ordinary skill in the art, including direct modulation of acarrier using D/A converters, a I/Q modulator, and a filter or digitalup conversion using an NCO and a digital multiplier followed by a D/Aconverter and filter. The plurality of modulated analog signals 614 arepreferably post-processed, including, but not limited to amplificationby one or more amplifiers 617, and most preferably an analog inverse ofthe digital transformation provided by the digital transform matrix 210of FIG. 2 with an analog transform matrix 618, and transmitted with asingle or multiple antenna configuration (not shown) to the userequipment 106 as shown in FIG. 1.

It should be appreciated that the present invention provides numerousdesirable features including maintenance of signal fidelity bytransmitting a digital representation of the signal that is thenconverted in the satellite to an analog signal, which is subsequentlytransmitted to user equipment, rather than transmitting an analog signalto the satellite for transmission to the user equipment. In this way,fading on the uplink from the earth terminal to the satellite is notcorrelated with the amplitude on the downlink. Furthermore, because thefidelity is maintained by the present invention, the signals can bemathematically manipulated at the earth terminal and/or the satellite inorder to perform beam forming as the amplitude and phase characteristicsbetween feed elements is maintained with the present invention. Inaddition, by adaptively block scaling each of the digital data streams,the RF bandwidth of the gateway link is minimized while maximizing thedynamic range. Each of the carrier/beam channels is independent with theseparate digital data stream representations. Also, a large channel isless likely to cause an increase in the noise floor of another channel,and large dynamic range differences are supported between beams andcarriers since each has its own individual exponent, thereby keeping thechannels relatively independent. In accordance with the presentinvention, other desirable features are present such as within a singlebeam and carrier, the dynamic range and signal fidelity can beindividually adjusting by varying the size of the mantissa, and bymultiplexing the digital data streams, failed components on thesatellite can easily be routed using alternative paths and/or sparecomponents inserted. The use of a digital data stream and digitallyimplemented transform operation also permits this transform math to bechanged to compensate for a failed power amplifier, change in amplifierperformance or change in the analog output transform. As little morethan a Digital to Analog conversion is being performed on the satelliteit can be built into a small, low power and hence to support arelatively low satellite price, and digital circuits are inherentlyrepeatable where analog circuits are not, reducing the manufacturing andtest times and hence the payload cost.

In addition to the foregoing, the methods and apparatus presentsignificant benefits that would be apparent to one or ordinary skill inthe art. Furthermore, while a preferred exemplary embodiment has beenpresented in the foregoing description of the drawings, it should beappreciated that a vast number of variations in the embodiments exist.Lastly, it should be appreciated that these embodiments are preferredexemplary embodiments only, and are not intended to limit the scope,applicability, or configuration of the invention in any way. Rather, theforegoing detailed description provides those skilled in the art with aconvenient road map for implementing a preferred exemplary embodiment ofthe invention. It being understood that various changes may be made inthe function and arrangement of elements described in the exemplarypreferred embodiment without departing from the spirit and scope of theinvention as set forth in the appended claims.

1. An apparatus for coupling an earth terminal to a satellite,comprising: a plurality of inputs of the earth terminal configured toreceive a plurality of digital communication signals; an autoscalingdigital multiplexer of the earth terminal configured to digitallymultiplex said plurality of digital communication signals to produce adigital composite signal; a digital modulator of the earth terminalconfigured to digitally modulate said digital composite signal toproduce a digitally modulated composite signal; an input of thesatellite configured to receive said digitally modulated compositesignal; a digital demodulator of the satellite configured to digitallydemodulate said digitally modulated composite signal received by saidinput of the satellite to produce a second digital composite signal; aautoscaling digital demultiplexer of the satellite configured todigitally separate said second digital composite signal into a secondplurality of digital communication signals; and a modulator of thesatellite configured to modulate said second plurality of digitalcommunication signals to produce a plurality of modulated analogsignals.
 2. The apparatus for coupling the earth terminal to thesatellite of claim 1, wherein said plurality of digital communicationsignals are Third Generation Partnership Project (3GPP) Wideband CodeDivision Multiple Access (WCDMA) Direct Sequence Spread Spectrum (DSSS)signals.
 3. The apparatus for coupling the earth terminal to thesatellite of claim 1, further comprising a digital transform matrix ofthe earth terminal that is configured to digitally transform saidplurality of digital communication signals.
 4. The apparatus forcoupling the earth terminal to the satellite of claim 3, wherein saiddigital transform matrix is a Fourier transform matrix.
 5. The apparatusfor coupling the earth terminal to the satellite of claim 3, whereinsaid digital transform matrix is a Butler transform matrix.
 6. Theapparatus for coupling the earth terminal to the satellite of claim 1,wherein the autoscaling digital multiplexer of the earth terminalcomprises: a processor configured to generate a sealing vector for saidplurality of digital communication signals; an operator configured toproduce a mantissa for each of said plurality of digital communicationsignals with said scaling vector and said plurality of digitalcommunication signals; and a multiplexer configured to multiplex saidmantissa for each of said plurality of digital communication signals andsaid scaling vector to produce said digital composite signal.
 7. Theapparatus for coupling the earth terminal to the satellite of claim 6,wherein said processor is configured to encode said scaling vector. 8.The apparatus for coupling the earth terminal to the satellite of claim6, wherein said processor is configured to: determine a minimum exponentof said scaling vector; calculate a difference between each of theexponents of said scaling vector and said minimum exponent; and form anencoded scaling vector from said minimum exponent and said differencebetween each of the exponents of said scaling vector and said minimumexponent.
 9. The apparatus for coupling the earth terminal to thesatellite of claim 6, wherein said processor is configured to: determinea maximum exponent of said scaling vector; calculate a differencebetween said maximum exponent of said scaling vector and each of theexponents of said sealing vector; and form an encoded sealing vectorfrom said maximum exponent and said difference between said maximumexponent and each of the exponents of said scaling vector.
 10. Theapparatus for coupling the earth terminal to the satellite of claim 6,wherein said processor is configure to perform a Huffman encoding toencode said scaling vector.
 11. The apparatus for coupling the earthterminal to the satellite of claim 6, wherein said multiplexer isconfigured to Time Division Multiplexing (TDM) said mantissa for each ofsaid plurality of digital communication signals and said scaling vector.12. The apparatus for coupling the earth terminal to the satellite ofclaim 1, further comprising an encryptor configured to encrypt thedigital composite signal.
 13. The apparatus for coupling the earthterminal to the satellite of claim 1, wherein said autoscaling digitaldemultiplexer of the satellite comprises: a demultiplexer configured toseparate a plurality of mantissas and an encoded scaling vector fromsaid second digital composite signal; a processor configured to decodethe encoded scaling vector to produce a scaling vector for each of saidplurality of mantissas; and an operator configured to produce saidsecond plurality of digital communication signals with said plurality ofmantissas and said scaling vector.
 14. The apparatus for coupling theearth terminal to the satellite of claim 1, further comprising an analogtransform matrix configured to transform said plurality of modulatedanalog signals into a plurality of transformed analog signals.
 15. Anmethod for coupling an earth terminal to a satellite, comprising:receiving a plurality of digital communication signals with a pluralityof inputs of the earth terminal; digitally multiplexing said pluralityof digital communication signals with an autoscaling digital multiplexerof the earth terminal to produce a digital composite signal; digitallymodulating said digital composite signal with a digital modulator of theearth terminal to produce a digitally modulated composite signal;receiving said digitally modulated composite signal with an input of thesatellite; digitally demodulating said digitally modulated compositesignal with a digital demodulator of the satellite to produce a seconddigital composite signal; digitally separating said second digitalcomposite signal into a second plurality of digital communicationsignals with an autoscaling digital demultiplexer of said satellite; andmodulating said second plurality of digital communication signals with amodulator of the satellite to produce a plurality of modulated analogsignals.
 16. The method for coupling the earth terminal to the satelliteof claim 15, wherein said plurality of digital communication signals areThird Generation Partnership Project (3GPP) Wideband Code DivisionMultiple Access (WCDMA) Direct Sequence Spread Spectrum (DSSS) signals.17. The method for coupling the earth terminal to the satellite of claim15, further comprising digitally transforming said plurality of digitalcommunication signals with a digital transform matrix of the earthterminal.
 18. The method for coupling the earth terminal to thesatellite of claim 17, wherein said digital transform matrix is aFourier transform matrix.
 19. The method for coupling the earth terminalto the satellite of claim 17, wherein said digital transform matrix is aButler transform matrix.
 20. The method for coupling the earth terminalto the satellite of claim 15, wherein said digitally multiplexing saidplurality of digital communication signals with said autoscaling digitalmultiplexer of the earth terminal to produce said digital compositesignal, comprises: generating a scaling vector for said plurality ofdigital communication signals; producing a mantissa for each of saidplurality of digital communication signals with said scaling vector andsaid plurality of digital communication signals; and multiplexing saidmantissa for each of said plurality of digital communication signals andsaid scaling vector.
 21. The method for coupling the earth terminal tothe satellite of claim 20, further comprising encoding said scalingvector.
 22. The method for coupling the earth terminal to the satelliteof claim 20, further comprising: determining a minimum exponent of saidscaling vector; calculating a difference between each of the exponentsof said scaling vector and said minimum exponent; and forming an encodedscaling vector from said minimum exponent and said difference betweeneach of the exponents of said scaling vector and said minimum exponent.23. The method for coupling the earth terminal to the satellite of claim20, further comprising: determining a maximum exponent of said scalingvector; calculating a difference between said maximum exponent of saidscaling vector and each of the exponents of said scaling vector; andforming an encoded scaling vector from said maximum exponent and saiddifference between said maximum exponent and each of the exponents ofsaid scaling vector.
 24. The method for coupling the earth terminal tothe satellite claim 23, further comprising performing a Huffman encodingto encode said scaling vector.
 25. The method for coupling the earthterminal to the satellite of claim 20, wherein said multiplexing is aTime Division Multiplexing (TDM) of said mantissa for each of saidplurality of digital communication signals and said scaling vector. 26.The method for coupling the earth terminal to the satellite of claim 15,further comprising encrypting said digital composite signal.
 27. Themethod for coupling the earth terminal to the satellite of claim 15,wherein said digitally separating said second digital composite signalinto a second plurality of digital communication signals comprises:separating a plurality of mantissas and an encoded scaling vector fromsaid second digital composite signal; decoding the encoded scalingvector to produce a scaling vector for each of said plurality of scalingvectors; producing said second plurality of digital communicationsignals with said plurality of mantissa and said scaling vector.
 28. Themethod for coupling the earth terminal to the satellite of claim 15,further comprising transforming said plurality of modulated analogsignals into a plurality of transformed analog signals with an analogtransform matrix.
 29. A communication system, comprising: an earthterminal comprising: a plurality of inputs configured to receive aplurality of digital communication signals; a autoscaling digitalmultiplexer configured to digitally multiplex said plurality of digitalcommunication signals to produce a digital composite signal; and adigital modulator configured to digitally modulate said digitalcomposite signal to produce a digitally modulated composite signal; anda satellite coupled to said earth terminal with said digitally modulatedcomposite signal, said satellite comprising: an input configured toreceive said digitally modulated composite signal; a digital demodulatorconfigured to digitally demodulate said digitally modulated compositesignal received by said input to produce a second digital compositesignal; a autoscaling digital demultiplexer configured to digitallyseparate said second digital composite signal into a second plurality ofdigital communication signals and a modulator configured to modulatesaid second plurality of digital composite signal to produce a pluralityof modulated analog signals.
 30. The communication system of claim 29,wherein said plurality of digital communication signals are ThirdGeneration Partnership Project (3GPP) Wideband Code Division MultipleAccess (WCDMA) Direct Sequence Spread Spectrum (DSSS) signals.
 31. Thecommunication system of claim 29, said earth terminal further comprisinga digital transform matrix that is configured to digitally transformsaid plurality of digital communication signals.
 32. The communicationsystem of claim 31, wherein said digital transform matrix is a Fouriertransform matrix.
 33. The communication system of claim 31, wherein saiddigital transform matrix is a Butler transform matrix.
 34. Thecommunication system of claim 29, wherein said autoscaling digitalmultiplexer comprises: a processor configured to generate a scalingvector for said plurality of digital communication signals; an operatorconfigured to produce a mantissa for each of said plurality of digitalcommunication signals with said scaling vector and said plurality ofdigital communication signals; and a multiplexer configured to multiplexsaid mantissa for each of said plurality of digital communicationsignals and said scaling vector to produce said digital compositesignal.
 35. The communication system of claim 34, wherein said processoris configured to encode said scaling vector.
 36. The communicationsystem of claim 34, wherein said processor is configured to: determine aminimum exponent of said scaling vector; calculate a difference betweeneach of the exponents of said scaling vector and said minimum exponent;and form an encoded scaling vector from said minimum exponent and saiddifference between each of the exponents of said scaling vector and saidminimum exponent.
 37. The communication system of claim 34, wherein saidprocessor is configured to: determine a maximum exponent of said scalingvector; calculate a difference between said maximum exponent of saidscaling vector and each of the exponents of said scaling vector; andform an encoded scaling vector from said maximum exponent and saiddifference between said maximum exponent and each of the exponents ofsaid scaling vector.
 38. The communication system of claim 34, whereinsaid processor is configure to perform a Huffman encoding to encode saidscaling vector.
 39. The communication system of claim 34, wherein saidmultiplexer is configured to Time Division Multiplexing (TDM) saidmantissa for each of said plurality of digital communication signals andsaid scaling vector.
 40. The communication system of claim 29, furthercomprising an encrytor configured to encrypt the digital compositesignal.
 41. The communication system of claim 29, wherein saidautoscaling digital demultiplexer comprises: a demultiplexer configuredto separate a plurality of mantissas and an encoded scaling vector fromsaid second digital composite signal; a processor configured to decodethe encoded scaling vector to produce a scaling vector for each of saidplurality of mantissas; and an operator configured to produce saidsecond plurality of digital communication signals with said plurality ofmantissas and said scaling vector.
 42. The communication system of claim29, further comprising an analog transform matrix configured totransform said plurality of modulated analog signals into a plurality oftransformed analog signals.